Immunoassays have been used in recent years to detect the presence of infectious diseases. In order for the assay to be useful, it must detect a particular organism with a high degree of reliability. In most cases, this requires the isolation and reaction of antigens peculiar to the organism with corresponding antibodies. For the test to be commercially successful, it also needs to be relatively inexpensive, long-keeping, simple to use and rapid.
One such organism which can be detected by immunoassay is Chlamydia trachomatis (herein C. trachomatis) which is one of two microbial species of the genus Chlamydiaceae, order Chlamydiales. There are 15 or more serotypes of this species which are the causes of a number of human ocular and genital diseases including trachoma, inclusion conjunctivitis, lymphogranuloma venereum, nongonococcal urethritis and proctitis. Infection from C. trachomatis is pervasive in the general population since it is believed that there are millions of cases each year of nongonococcal urethritis alone.
Gonorrhea is a disease usually transmitted by sexual contact caused by a bacterium of the Neisseria genus, especially N. gonorrheae. The disease has plagued mankind for thousands of years, and although antibiotics have helped control its spread, it still persists in epidemic proportions in many parts of the world. The importance of detection and treatment of this disease is well recognized. N. meningitidis and N. lactamica are also species of considerable medical and diagnostic interest.
Because of the widespread nature of these diseases, there is considerable interest in having a rapid, simple and reliable test for detection of chlamydial and gonococcal organisms. Assays for C. trachomatis and N. gonorrheae carried out using a solid support are described in U.S. Pat. Nos. 4,497,899 (issued Feb. 5, 1985 to Armstrong et al) and 4,497,900 (issued Feb. 5, 1985 to Abram et al). The described assays are performed by extracting antigen from the organism and coating it on a bare solid support. The coated antigen is then detected with either one or two antibodies, one of which is suitably labeled. The critical feature of the assays appears to be the use of a solid support for attachment which is untreated or uncoated with any material. Attachment of antigen is apparently achieved by incubating the coated support for an extended time sufficient to cause adsorption of antigen thereon. The entire assay described in U.S. Pat. No. 4,497,899 takes at least 3 hours to perform.
A much more rapid test for chlamydial or gonococcal organisms which has high reliability and can be performed at room temperature is described and claimed in U.S. Ser. No. 255,923 (filed on Oct. 7, 1988 by Pronovost). Our colleague found that ionically charged (specifically cationic) supports attract chlamydial or gonococcal antigen and enable one to quickly and sensitively detect the antigen.
A further improvement is described in U.S. Ser. No. 255,920 (filed Oct. 7, 1988 by Mauck and issued July 16, 1991 as U.S. Pat. No. 5,032,504) which describes the use of a surfactant-coated uncharged membrane in chlamydial assays. That invention enables one to rapidly and sensitively detect the antigen in biological specimens that contain copious amounts Of whole blood, mucus or components thereof.
Still another advance is described in U.S. Ser. No. 366,100 (filed June 14, 1989 by Mauck et al) in which chlamydial antigen is detected in an assay using a microporous filtration membrane having surface hydroxy groups. Such membranes exhibit increased keeping properties and thus provide significant marketing and user advantages.
The current product marketed by Kodak as the SURECELL.TM. Chlamydia Test Kit has been received by the marketplace quite positively. One of the reasons for this is the presence of positive and negative controls within the test device used for the assay. This device contains a surfactant-coated BIODYNE.TM. polyamide membrane like that described in U.S. Ser. No. 255,920 (noted above) in the test wells used for both the controls and assay of the unknown. This membrane is nonionic and has no hydroxy or ionic groups on its surface.
It was found in manufacturing this test kit that frequently the positive control well did not have adequate and uniform coverage of reagents when they were deposited using automated equipment. Particularly, antigen placed within the positive control well was not uniformly distributed on the membrane unless deposition was carefully done by hand using large volumes of fluid. It was thus desirable to find a way to rapidly and uniformly incorporate the needed reagents in the positive control well using automated means and without large volumes of fluid.